U.S. Pat. No. 3,857,398 to Rubin, entitled "Electrical Cardiac Defibrillator", describes a combined cardiac pacer and defibrillator device which performs a pacing or a defibrillating function depending on the condition detected. When the device detects tachycardia, it switches to a defibrillating mode and, after a period of time during which a charge is accumulated, delivers a defibrillation shock to the patient. When the device detects that the heart rate has fallen below a predetermined value, the pacer switches to a demand pacing mode and delivers pacing pulses to the heart.
A multiprogrammable, telemetric, implantable defibrillator is disclosed in the copending U.S. patent application Ser. No. 576,178 of Norma Louise Gilli et al., filed AUG. 29, 1990, entitled "Reconfirmation Prior To Shock In Implantable Defibrillator". This device contains a bradycardia support system as well as a high energy shock system to revert ventricular tachycardia to normal sinus rhythm. After reconfirmation of the presence of a tachycardia, high energy shock is delivered to the patient either at a predetermined time or when the desired energy level is reached.
Although technological improvements in implantable arrhythmia control devices have been made, a number of problem areas remain. Significant among these is the false triggering of electrical discharges in some instances of benign supraventricular tachycardia, for example sinus tachycardia with aberrant conduction. Such unnecessary discharges result in discomfort and potential danger to the patient.